Silencer for high frequency sounds



April 10, 1956 5. BROWN ET AL 2,741,325

SILENCER FOR HIGH FREQUENCY SOUNDS Filed July 25, 1952 N Mua M r MW MS m 5 DE 4 R6 M 1 may R W I x M M w United States Patentfi SILENCER FOR HIGH FREQUENCY SOUNDS Richard E. Brown, Cleveland, and George M. Walton,

Shaker Heights, Ohio, assignors to Air-Maze Corporation, Cleveland, Ohio, a corporation of Delaware Application July 25, 1952, Serial No. 300,934

4 Claims. (Cl. 181-50) This invention relates to improvements in a silencer for use with a stream of air or other gas flowing to a fan, blower, supercharger or the like.

One of the objects of the present invention is to provide a silencing device adapted to silence sound waves of the order of 2000 cycles per second and higher.

Another object of the present invention is to provide a novel device for silencing sound waves of the order of 800 to 2000 cycles per second.

Other objects and advantages of our invention will be apparent from the accompanying drawings and description and the essential features will be set forth in the appended claims.

In the drawings,

Fig. l is an end'elevational view of one embodiment of our invention;

Fig. 2 is a transverse sectional view of the same taken along the line 2--2 of Fig. 1; while Fig. 3 is a bottom plan view of the device of Figs. 1 and 2.

A typical use of our invention is in combination with a turbine driven air supercharger wherein a gas turbine drives the air supercharger which in turn is connected to the outlet of our device. In apparatus of this type, very high pitched sounds are transmitted back along the air stream through the outlet tube 10. These sounds are of the order of 2000 cycles per second and higher. We find that a silencer constructed according to the present invention will reduce such sounds to an acceptable audible level. This is true, however, only if the critical points in our construction are adhered to.

Our improved silencer comprises a main housing 11 to which the outlet tube 10 is rigidly attached at one end as clearly shown in Figs. 1 and 2 of the drawings. The upper portion of the main housing indicated at 11a comprises a generally semi-cylindrical wall coaxial with the outlet tube 10. Other straight wall portions 11b extend tangentially from the ends of the portion 11a to a flat bottom wall 110. The end wall 11d, to which the outlet tube is connected, is uninterrupted except for a round opening 12 registering with the outlet tube 10. The opposite end wall 112 is imperforate. The bottom wall 11c is imperforate except for a large circular opening 13 which provides the inlet for the housing. Around this opening are provided a series of fixed nuts 14 in a circle so that the flange of an inlet pipe may be secured thereto.

The walls 11a and 11b are covered on the interior with a sound absorbing material indicated at 15. The walls 11c, 11d and 112 need not be covered with this sound absorbing material for eflicient silencing.

An end pad 16 of sound proofing material is substantially circular in form as clearly indicated in Fig. l and is spaced from the outlet opening 12 and extends crosswise of the housing 11 parallel to the end walls 11a and ice lle, or at right angles to the axis of the outlet tube 10. It will be noted in Fig. 2 that thepad 16 lies wholly on the outlet side of the inlet opening 13 when projected into the housing 11 at right angles to the bottom plate 11g. We find that this location of'the bottom pad 16'on the outlet side of the inlet opening 13 (as projected) is critical to get the best results from our equipment.

The sound proofing material indicated at 15 and 16 may be of felt, cotton, or other similar material.

The pad 15 is held in place by a stilt, perforate sheet 18 extending over the entire area of pad 15 and resting on V-shape flanges 19 welded to end walls 11d and 11a. The sheet 18 may be flattened expanded metal backed up by a sheet of screen wire mesh 20.

The pad 16 is held in place by a plurality of spacer bars 17, three being shown. These spacer bars are rigidly fixed to the end wall 11d and firmly secured to an imperforate circular plate 21. An annular ring 22 is welded to the periphery of plate 21 and extends at right angles thereto. This ring has a flange 22a parallel to and spaced from plate 21. Pad 16 is held against plate 21 by expanded metal sheet 23 lying behind flange 22a. A sheet 24 of screen wire mesh may be interposed between sheet 23 and pad 16.

We find that for the best results from our equipment the generally annular area A indicated on Fig. 2 as lying between the pad 16 and the walls 11a, 11b, and 11c should equal the area of the inlet opening 13.

While the spacing between the pad 16 and the end wall 11d may vary somewhat, we prefer to keep the annular opening B between the periphery of pad 16 and the end wall lid to approximately one hundred and fifty per cent of the outlet area C measured at the inside diameter of tube 10.

To improve air flow, a semi-toroidal ring 25 is preferably secured to the inner face of Wall 11d closely surrounding the outlet opening 10.

It will be noted that air entering in the direction of the arrow at the inlet opening 13 and departing in the direction of the arrow at the outlet tube 10, makes a ninety degree turn. We find that our device provides a very satisfactory substitute for an elbow in close quarters where such a ninety degree turn is essential while at the same time providing silencing for the very high pitched sounds which travel backward on the incoming air stream from the turbo-charger.

What we claim is:

l. A silencer for a stream of air or the like comprising a housing generally D-shape in section having a semicylindrical top and sidewalls tangential to said top and having two flat end walls and a flat bottom wall, there being a cylindrical outlet through one of said end walls coaxial with said semi-cylindrical top, there being a circular inlet opening through said bottom wall spaced from said outlet end wall, sound absorbing material covering the inside of said top and side walls, a generally circular pad of sound absorbing material in said housing spaced from said outlet end wall and generally parallel thereto, said pad being spaced from said top and side and bottom walls, means supporting said pad in said housing, and said pad lying on the outlet side of said inlet opening projected into said housing at right angles to said bottom wall.

2. The combination of claim 1 wherein the area measured between the edge of said pad and said top and side and bottom walls in the plane of said pad is approximately equal to the area of said inlet opening.

3. The combination of claim 2 wherein said pad is sub: 7 a

stantially equally spaced from said top and bottom walls.

4. The combination of claim 3 wherein the area of the annular space between the periphery of said pad and said end wall measured at right angles to said end wall is approximately one hundred and fifty per cent of the area of said outlet.

References Cited in the file of this patent I V UNITED STATES PATENTS 1,769,778 Field July 1, 1930 4 Jackv May 5, 193 6 FOREIGN PATENTS Great Britain June 29 ,1931 Austria May 25, 1938 Germany Jan. 6, 1942 

